Rhabdo may sound like a cool name, but it’s actually a really, really not cool medical condition brought on by excessive physical demands. You may have seen a few articles pop up here and there in newspapers like the New York Times labeling it as a harmful side effect of high intensity exercise. I’ve also seen countless social media posts giving high intensity exercise a lot of flack for causing rhabdo. So I’ve decided to clear up a few things about both rhabdo and high intensity exercise.

What is Rhabdo?

Rhabdo, short for rhabdomyolysis (which literally means dissolution of skeletal muscle), results when muscle fibers get injured, die, and release harmful substances into the bloodstream. It’s not just painful, but a serious medical condition needing proper medical attention. Rhabdo can be caused by many things, including trauma (e.g., a car crash, electric shock injury, or venom from a snake bite), the use of alcohol or illegal drugs, the use of certain medications, hyperthermia or heat stroke, seizures, a metabolic disorder, diseases of the muscles, viral and bacterial infections, and extreme muscle strain especially in untrained athletes.

Severe muscle strain brought on by exercise can cause rhabdo, but so can a host of other things. We wouldn’t tell people not to take certain medications (like antipsychotics or statins) just because there’s a small risk of rhabdo. So why would we tell people not to do a certain type of exercise? Discussed in more detail below, high intensity exercise in particular has incredible health benefits and, when done properly, is safe for virtually anyone. (And I emphasize, when done properly!).

Benefits of High Intensity Exercise

High intensity exercise has countless benefits. In addition to all the benefits of exercise in general, high intensity exercise:

Burns more calories (and more fat) in less time than traditional exercise formats

Increases calorie burn for up to 48 hours after the workout

Is better at helping you lose fat mass

Is anabolic and therefore promotes muscle development (unlike steady state cardio)

Can still improve oxygen consumption even though it’s not a long steady state exercise

Can reduce resting heart rate and blood pressure

Helps regulate blood sugar better than steady state cardio

Can be adapted to just about any type of exercise, including lifting weights, running, cycling, swimming, etc.

That’s a long list, and rightfully so. High intensity exercise is actually really healthy and effective at promoting weight loss, muscle development, and overall health and fitness. It’s also safe for almost all people when it’s specifically designed for the individual’s fitness level. This is an important point because most high intensity exercise classes are not designed to accommodate all individual fitness levels even though they are marketed to both conditioned and de-conditioned consumers.

Rhabdo and High Intensity Exercise

If high intensity exercise is so good for us, why have seen an uptick in exercise-induced rhabdo over the past several years? The answer is simple. People are engaging in physical activity that their bodies are not prepared or conditioned for. This is particularly true for our weekend warriors who shock their bodies with 2-3 hours of high intensity exercise, e.g., spin class, over the course of 2-3 days and then virtually no physical activity during the week. Or our cross-fitters who have not been on a regular exercise program in over 6 months (or sometimes ever) and jump right in to fast reps with heavy weight that their body is not ready for. Another concern is the length of time people are spending performing high intensity exercise in a single bout. High intensity exercise is meant to be performed for shorter durations, the exact duration depending on the level of intensity. Doing an intense hour-long spin class is not necessarily healthy unless you are conditioned such that your heart rate does not exceed a certain level for too long.

Although even elite athletes are not immune to rhabdo, it is generally preventable when it comes to exercise. It makes sense that elite athletes are at a higher risk for rhabdo because of the intense strain they put on their bodies on a daily basis. Ideally, the average person’s risk for rhabdo should be less than an elite athlete because the average person does not need to put the same strain on his or her body.

For a deconditioned individual, even a brisk walk could reach the level of high intensity if the person’s heart rate reached 70-80% of his or her max. Yet we see these people in spin class, cross-fit, and even Zumba all the time. It might be fine if these classes could be modified for different fitness levels, but often times they’re not. So of course many people’s risk of rhabdo is going to sky rocket. Dangers arise for more fit individuals as well. If you’re maintaining your heart rate at 70+% of your max heart rate for more than several minutes at a time, you could be at risk.

Preventing Rhabdo

BUT rather than avoid high intensity exercise because of this risk of rhabdo, here are few things you can do to decrease your risk and still reap the benefits of high intensity exercise:

Establish a base level of fitness before engaging in high intensity exercise. If you are not already doing 20-60 minutes of moderate physical activity most days a week, you probably should not dive into high intensity just yet.

Get your physician’s clearance before starting a high intensity training program to make sure you don’t have any contraindications or restrictions that you should abide by. This is particularly important for people with chronic disease or medical conditions like heart disease, diabetes, high blood pressure, history of stroke, arthritis, etc.

Know your max heart rate and, therefore, your target heart rate for low, moderate, and high and super high intensity exercise. There are a few formulas to estimate your max heart rate, but the best way would be to have a qualified fitness or athletic professional administer a maximum heart rate test. Then use the appropriate percentage of your maximum heart rate to determine a target range for the level of intensity you want to do.

Perform high intensity exercise for no more than 20-25 minutes at a time or in intervals ranging from 15 seconds to 4-6 minutes depending on the intensity followed by an active recovery period of appropriate duration. For example, if you do a 15-30 second all out sprint, allow about 3-4 minutes for recovery starting out. If you do a sub-maximal intensity interval, start with a recovery period equal or even slightly longer in duration than the high intensity interval.

Consult a fitness professional to help you design an appropriate program for your fitness level and goals.

Once you do start a program involving high intensity exercise, continue doing moderate intensity exercise on other days. Avoid high intensity exercise if you are planning on remaining a “weekend warrior” as this increases your risk for rhabdo and other injuries.

Most importantly, listen to your body. If something doesn’t feel right, don’t keep pushing yourself. If you feel pain, decrease intensity. Don’t do things that your body isn’t ready for yet — instead, set goals, have a plan, and work towards that. And always allow yourself to recover fully after a high intensity workout. High intensity exercise can be performed from 1-4 times a week depending on level of training.